Which smartphone operating system really is the best? More important, which one is best for you?

If you're in the market for a new smartphone, choosing which one to buy has much to do with the operating system that runs the phone as with the hardware itself. To help you decide, I put the latest versions of the three top mobile operating systems through their paces: Android 2.3, Windows Phone 7 and iOS 4.3.

There are, of course, two other smartphone operating systems out there: RIM's BlackBerry OS and Hewlett-Packard's webOS. However, we decided not to include them at this point.

Although RIM still has a considerable presence, its market share has been plunging, dropping from nearly 36% to just over 30% in the most recent quarter, and its developer support has been anemic, with an estimated 20,000 apps available even though it's been around for far longer than the iPhone and Android platforms, each of which has hundreds of thousands apps. (Windows Phone 7, which was launched just last October, has about 9,500 apps.) In other words, it no longer feels like a contender.

If BlackBerry makes a comeback, we'll include it in our next roundup. We'll also be watching HP's webOS, which will be available on several new devices this summer.

In this roundup, I concentrated as much as I could on the underlying operating systems, not the hardware on which they run. To get the truest look at Android, I tested it using a Samsung Nexus S, which ships with a version of Android that hasn't been customized by either the device maker or the service provider -- it's Android as Google intended it. For a look at Windows Phone 7, I chose the HTC Surround. And for iOS, I looked at the iPhone 4.

I've compared the platforms in several different categories, including ease of use, app availability, features, integration with desktop and Web-based apps, customization and platform openness. Come along for the ride and see if you agree.

User interface

Apple stuck to its decades-long recipe for success when designing iOS -- keep it simple and elegant, and marry the hardware to the operating system in as seamless a way as possible. Google, meanwhile, true to its techie roots, gives you an operating system you can tweak and customize to your heart's content, although that also means you may sometimes get confused along the way.

Microsoft made what may be the biggest gamble of all, by designing a phone that puts accessing information, rather than running apps, center stage.

Android

Like iOS, Android is app-centric, and so it features app icons front and center. The home screen is simple and stripped down -- all the app icons can be moved or deleted, except for three unmovable icons: the Dialer (for making a phone call), the Application Tray (an overlay that shows you all your apps) and the Web app.

There are also four hard buttons across the bottom of each Android device for bringing up a context menu, returning to the Home screen, going back a screen and performing a search.

As shipped by Google, Android includes five built-in panes, including the home screen. You can move among them by either sliding your finger to the left or right, or by touching a dot at the bottom of the screen that represents one of the panes. Each of these panes can be customized by adding widgets, shortcuts and files. So, for example, you can devote one pane to social networking apps and communications, another to news and feeds, another to entertainment and so on.

Overall, the interface is simple and straightforward. But at times it also has the feel of being not quite baked -- a little rough around the edges. It's as if the designers were still taking whacks at finalizing the design.

For example, there are inconsistencies in the way Android performs familiar tasks. Take the way it handles Contacts. Run the Contacts app by tapping its icon, and you'll come to a complete list of contacts, including those imported from Gmail, those you've input on the phone itself, and contacts from social networking sites such as Facebook.

If you run the Dialer app (to make a phone call) and then tap Contacts from inside the Dialer, you'll come to what looks like the identical Contacts list -- but that list does not include your contacts from social networking sites. Nowhere are you warned that they're not truly identical.

You may also have trouble finding some of Android's interesting features. For example, Android's Universal Inbox is extremely useful -- it puts all of the e-mail from all of your accounts into a single location. But finding it isn't especially easy. First you have to find the Messaging app, and from there the Universal Inbox. You would expect a Universal Inbox for e-mail to live in the E-mail app, but it's not there.

iOS

It's like this: If you want the most elegant, best-integrated marriage of hardware and software -- not to mention absolute simplicity when it comes to ease of use -- you want the iPhone.

This is the phone that launched the smartphone revolution (yes, the BlackBerry may have gotten there sooner, but the iPhone perfected it), and for style and ease of use, it can't be beat.

Apple's iOS interface is the iconic design that people have come to associate with smartphones: a spare screen with app icons arrayed in a clean grid, a single hard button at the bottom of the phone that returns you to the main screen, and tiny notification icons across the top that inform you about things such as whether you have a 3G connection, your connection strength, battery level and so on.

At the very bottom of the screen, above the hard button, are icons for the most important apps, the ones for things like sending e-mail and making phone calls. Because apps are front and center, it's easy to choose the app you want to run.

You can have up to 11 home screens with their own apps and folders. And you can drag and drop icons between screens -- you hold and press an icon until all of the icons shake, then drag the icon to the screen where you want it to live. You can group multiple apps into folders as well.

Windows Phone 7

The most well-known of the slogans Apple has used over the years is probably "Think different" -- but when it comes to smartphone interfaces, Microsoft is the one thinking differently. Whether you like that new way of thinking will determine whether you'll be a fan of Windows Phone 7.

Rather than taking an app-centric approach, as the iOS and Android platforms do, Windows Phone 7 is organized around a series of hubs -- displayed as tiles -- that deliver information to you or let you perform certain tasks. So when you fire up a Windows Phone 7 device, you won't be greeted by a screen full of app icons but a collection of large tiles.

In some instances, the tiles are little more than big buttons that, when tapped, launch standard apps for, say, e-mail. However, others deliver updates on changing information, such as the activity of your friends on Facebook, the number of unread messages in your e-mail account or the next upcoming appointment on your calendar. That's why the tiles are oversized, rather than being small icons -- they deliver useful information at a glance, without having to run the underlying app. If you're focused on getting information fast, this operating system is the easiest of all to use.

On the other hand, you get only two screens -- not seven, as you do with Android, or 11, as you get with the iPhone. All in all, the main interface and panes are the least customizable of any of the three phone operating systems.

There's another way that Windows Phone 7 differs from both iOS and Android -- instead of emphasizing how long you'll want to play with your smartphone, Microsoft 's ad campaign pushes the idea that Windows Phone 7 has been designed so that you'll spend less time on your phone. To a great extent, it delivers on that promise, but overall, Windows Phone 7 still isn't as intuitive, as elegantly conceived or as simple to use as iOS.

Conclusion

For simplicity, elegance and beautiful design, iOS has no peer. Android, while not badly designed, remains a bit rough around the edges. And Windows Phone 7 is designed to show information at a glance and isn't app-centric, so if you're the kind of person who isn't enamored with apps and just wants to get information fast, it's worth a look.

Apps and openness

You want apps? Android's got an estimated 100,000 of them and Apple's got even more; there are an estimated 350,000 apps available for iOS. The truth is, though, that as a practical matter, both operating systems have more apps than you'll ever need. Windows Phone 7, with about 9,500 apps, is still playing catch-up.

How you get apps on Android compared to the way you do it on iOS and Windows Phone 7 reflects the companies' different philosophies: Google has designed Android to be as open as possible, while Apple and, to a lesser extent, Microsoft, have decided to serve as gatekeepers.